JERUSALEM — Tens of thousands of Israelis on Saturday night protested in Tel Aviv against the new right-wing government’s plans to fundamentally overhaul the judicial system, accusing Prime Minister Benjamin Netanyahu of trying to weaken the country’s democratic institutions just weeks after returning to power.
The protest was organized by grass-roots activists and backed by the leaders of Israel’s centrist and left-wing opposition parties. The Israeli news media estimated a turnout of 80,000 people by 8:30 p.m., despite a steady rain, and thousands more joined protests in Jerusalem and Haifa.
The protests were an early indication of the backlash facing the government, the sixth led by Mr. Netanyahu, and a clear illustration of widening political division and polarization in Israel.
Mr. Netanyahu, barely three weeks after his government was sworn in, is seeking to curb the powers of the country’s Supreme Court and has argued that the top court has too much influence.
Critics call the move a power grab that would limit judicial independence and oversight and give politicians the upper hand in appointing judges and government attorneys.
Ehud Barak, a former Israeli prime minister and former army chief of staff, who attended the protest in Tel Aviv, said Mr. Netanyahu’s proposals would “crush” the judicial system.
“We won’t let that happen,” he said on Israeli television.
In and around Tel Aviv’s Habima square, many of the protesters carried umbrellas or placards. But others carried Israeli flags, the symbol of the modern Jewish state whose liberal democracy they believe is under threat.
Uri Kinrot, a resident of Beersheba, a city in the southern Negev desert, came to the demonstration in Tel Aviv with his three young children. “I am here of course for myself, but mainly for them,” he said, “to fight so that they can grow up in a democratic country that will give them equality and equal opportunities.”
Mr. Kinrot held a sign that read: “We are the fortress. We will not fall!” He said he was there to stop what he called a “dictatorship” taking over Israel.
Other protesters held placards with sharp messages warning of “fascism,” a “coup d’état” and corruption. Mr. Netanyahu is currently on trial on charges of corruption. One sign read: “We will die before giving up on democracy.”
The governing coalition, led by Mr. Netanyahu and his conservative Likud party, includes far-right and ultra-Orthodox parties. Widely considered the most right-wing and religiously conservative coalition in Israel’s history, it won a majority of 64 seats in the 120-seat Parliament in the November elections.
The government’s proposed changes include reducing the Supreme Court’s judicial oversight, including stripping it of the ability to strike down legislation that it deems unreasonable. The government also wants to change the way judges are chosen, and turn the legal advisers in government ministries into political appointees who would no longer answer to the attorney general.
The government is working rapidly to push through its reforms even as the Supreme Court is deliberating a petition to cancel the appointment of Aryeh Deri, a convicted felon, as a senior minister on grounds of “unreasonability.” Mr. Deri, a veteran politician and close Netanyahu ally, was recently convicted of tax fraud and, as part of a plea agreement, received a suspended prison sentence.
Many Israelis believe there is room for some carefully calibrated reform. But critics of the government say that such sweeping moves will turn Israel into a democracy in name only. The changes, they argue, will remove the protections the court provides for minorities and will put too much power in the hands of the government.
Israel has no formal constitution and only one house of Parliament, and the judicial plans have galvanized the opposition. The former prime minister and centrist leader of the opposition in Parliament, Yair Lapid, has described the proposed changes as constituting “extreme regime change” that would result in the elimination of Israel’s democracy.
In an extraordinarily forthright speech on Thursday, the president of the Supreme Court, Chief Justice Esther Hayut, said Mr. Netanyahu’s plan was designed to “deal a mortal blow to the independence of the judiciary and silence it.”
The new Likud minister of justice, Yariv Levin, excoriated Justice Hayut’s speech in a televised statement, accusing her of having joined activists in their call “to set the streets alight.”
Mr. Netanyahu released a video statement on Friday saying that the Israeli voters had given the government a clear mandate for carrying out judicial reform, and called for calm. The new rules would be made “responsibly and judiciously,” he said, and after reaching understandings through a process of dialogue in Parliament.
The protests on Saturday were also a test for the police.
The minister who oversees the police, the ultranationalist Itamar Ben-Gvir, had called for arrests and the use of water cannons against protesters who block roads, even though such operational decisions have always been the purview of senior police commanders on the ground.
Police commanders said they were committed to allowing peaceful protest to take place, and the police were only expected to intervene if protesters endangered the peace or broke the law. At the end of the protest a few hundred demonstrators blocked a main junction in Tel Aviv and tried to reach a major highway. The police contained them without resorting to water cannons.
Isabel Kershner reported from Jerusalem, and Ronen Bergman from Tel Aviv. Jonathan Rosen contributed reporting from Jerusalem.